This invention relates to an improved removable closure plate construction that is adapted for easy removal and provides a liquid-tight seal in an elongated floatable offshore hollow tubular column structure.
Closure plates are typically utilized in conjunction with offshore platforms having a subsurface structure referred to as a jacket. The jacket structure contains a plurality of tubular columns through which piles are driven during installation. Jackets which are too large to be lifted must be launched after transportation to an offshore installation site. Jackets are usually constructed on shore with temporary closure plates installed in the jacket legs or columns to render the structure buoyant. The closure plates are selectively located within the jacket columns so that the jacket floats in a predictable, stable position. To achieve a predictable, stable, flotation position, the closure plates must be placed in the columns to form flotation chambers which can be selectively flooded with water at the installation site to rotate the jacket to the proper upright position. When the jacket is in its proper upright position, the column closure plates are removed to provide substantially unobstructed access through which piles are driven to anchor the jacket to the ocean bed.
The object of the present invention is to provide an improved removable closure plate of the type disclosed in U.S. Pat. No. 3,613,381. In the prior art, the lower closure plate assembly is basically a truncated plate cone whose circumference is welded to the inside wall of a jacket column and when used in conjunction with an upper closure plate forms a flotation chamber. A chain is welded to the underside of the cone about its perimeter and the chain is attached to an eccentrically located pulling arm which extends through the cone. The closure plate is torn away from the column in segments by the application of a force to the pulling arm.
The present invention eliminates the eccentrically located pull arm and the chain welded to the underside of the closure plate as disclosed in the prior art. The improved removable closure plate, herein disclosed, centrally locates the pulling arm, is capable of resisting pressure from both sides and can be constructed of relatively thin metal for use in large diameter columns. Additionally, the improved removable closure plate is capable of resisting greater pressures for a comparable material thickness, is broken away from the column as a unit and develops a very large mechanical advantage for ease in removal.